The present invention relates to a method for torque and pitch control/adjustment for a wind power plant according to the rotational speed. The method serves to determine an optimal reference value for the generator torque according to the rotational speed for a pitch controlled wind power plant.
The wind power plant is started up by the control system in windy conditions, from a start-up wind rotational speed, and shut off again at high wind speed, the shut-off wind rotational speed, in order to prevent mechanical overload. The wind speed is, for example, detected via an anemometer or calculated from the rotational speed of the rotor and the power produced.
Pitch-controlled wind power plants operating at variable rotational speeds are known. During pitch control, the blade pitch of each rotor blade is adjusted about its longitudinal axis. At different blade pitches, the respective rotor blade collects a different torque from the wind.
For the control/adjustment of the wind power plant it is known to distinguish between two modes of operation. The first mode of operation is denoted as partial load operation in which the rotational speed is regulated by setting the torque. The second mode of operation is full load operation in which the rotational speed is regulated by adjusting the pitch.
In order to achieve optimal power output by the wind power plant, the rotational speed of the plant in the partial load range is set at the optimal ratio between the peripheral rotational speed of the rotor and the wind speed (λopt). The rotor blades are, therefore, set at a blade angle which generates the highest drive torque for the rotor shaft. The rotational speed of the rotor is set in the partial load range by the counter torque generated on the generator and/or convertor.
If, at a nominal wind speed, the maximum counter torque is reached on the generator, by further increasing the generator torque, the rotational speed may no longer be maintained at the operating point. An overload of the system is, therefore, avoided as the aerodynamic efficiency of the blades deteriorates and said blades are moved out of the optimum pitch. The specialist term for this process is also “to pitch”. The rotational speed of the rotor is thus influenced by the pitch of the blades after reaching the maximum generator torque.
A variable speed wind power plant is known from EP 1 007 844 B1, the entire contents of which is incorporated hereby by reference, which has a wound rotor induction generator. For operating the known wind power plant, a torque controller is known and a pitch controller which operates independently of the torque controller.
The technical object of the invention is to provide a method for torque and pitch control for a wind power plant according to the rotational speed, which delivers a particularly high output.